There are two types of earwax, wet and dry. Wet earwax is common in Africa and Europe, while dry earwax is characteristic of East Asian populations. South and Central Asian populations are half wet and half dry. Native Americans tend to have dry earwax. Nicholas Wade of the New York Times reported in January of last year that Japanese researchers have isolated the gene responsible for earwax differentiation. The curious thing is that earwax doesn't seem to be terribly important to human survival:

Since it seems unlikely that having wet or dry earwax could have made much difference to an individual's fitness, the earwax gene may have some other, more important function. Dr. Yoshiura and his colleagues suggest that the gene would have been favored because of its role in sweating.

They write that earwax type and armpit odor are correlated, since populations with dry earwax, such as those of East Asia, tend to sweat less and have little or no body odor, while the wet earwax populations of Africa and Europe sweat more and so may have more body odor. Several Asian features, like small nostrils, are conjectured to be adaptations to the cold. Less sweating, the Japanese authors suggest, may be another adaptation to the cold in which the ancestors of East Asian peoples are thought to have lived.

Cats and dogs liking earwax? Dogs will eat poo and rotten animal carcasses if given the chance... so it's not surprising (cats likley do as well they're just more secretive about - they have a reputation to uphold).